Data communication normally occurs on a network that is optimized for data transmission and is therefore physically adapted to be relatively immune to interference. However, some modern data communication scenarios overlay existing media and therefore may incorporate physical limitations dictated by the media. For example, one method of internetworking home computing or communication devices, such as multiple personal computers and peripherals, is to take advantage of the existing home telephone wiring system, which typically includes a network of wires to virtually every room in the house. This method is described, for example, by the presently active Home Phoneline Network Alliance (HomePNA) special interest group in its current version one (V1.x) standard, and its pending version two (V2.x) standard.
A limitation dictated by the advantageous use of the telephone lines within the home as a data network is that the telephone lines were not originally put in place to optimize data communications. Thus, the number and nature of bridge taps (associated with the connection of a telephone or another appliance to the network) are not readily controlled, as they vary with respect to the number of devices coupled to the network and the length of line associated with each bridge tap. Further, since each user's home can be different, a HomePNA system is preferably functional in a diverse set of environments. The chaotic set of environments within which a HomePNA system may function makes it difficult to configure a single system that will function properly in all, or most, environments. For example, each bridge tap, given the physics associated with the connection of a device to the network and the associated line length, may yield a spectral null within an important part of the transmission spectrum For a typical V2.x application, for example, bridge tap line lengths of fifteen to thirty-five feet will yield tap-induced spectral nulls within the 4-10 MHz band of interest. In addition to these tapp. induced spectral nulls, specific spectral nulls may be intentionally created to minimize interference with other communication media, such as ham radios.
These spectral nulls, however, may create a problem if one of them coincides, in the frequency domain, with a significant portion of a data transmission. Conventionally, a decision feedback equalized (DFE) is employed to recognize and correct for the signal loss associated with the transmission of data in a null. However, a DFE used in this manner leads to a complicated system that is difficult to start up (i.e., to converge for data recovery purposes). What is needed is a simplified receiver design that enables successful data transmission in the presence of spectral nulls, and in particular, in the presence of an unknown quantity and position of such nulls.